The present invention relates to a high-purity, heat-resistant oxynitride glass and a method of producing it, and more particularly to a method of producing oxynitride glass by using a block of fine silica powder (simply called "fine silica powder block") as a starting material and introducing it into an ammonia-containing gas at 800.degree. C. or higher in a reducing environment.
In the field of a semiconductor industry, semiconductors are subjected to a heat treatment such as doping, etc. In such a heat treatment process, high-purity, heat-resistant materials, which do not dissipate impurities even by heating, and which are not deteriorated at an operating temperature, are desired as supporting members for semiconductors.
For this purpose, silica glass produced by melting quartz powder is now utilized. However, impurities such as metals, etc. included in the starting quartz powder material tend to remain in the glass even after a purification process. Accordingly, the impurities such as metals are likely to be dissipated by diffusion from the supporting members made of the silica glass during the heat treatment process of semiconductors. Synthetic silica glass has a higher purity than the silica glass obtained by a melting method, but the synthetic silica glass is poor in heat resistance as compared to the silica glass obtained by a melting method, due to the influence of hydroxyl groups introduced at the time of synthesis of the silica glass. Thus, there is now no silica glass satisfying the requirements of both purity and heat resistance.
As glass excellent in purity and heat resistance, there is oxynitride glass, part of whose oxygen atoms are substituted by nitrogen atoms. It is known that the oxynitride glass has good mechanical properties, chemical properties, thermal properties, etc., and active research is now conducted on the improvement of the oxynitride glass.
Methods of producing oxynitride glass which have been reported so far include a method of blowing an ammonia gas into a molten glass, a method of melting a mixture of silicon nitride and a glass material. However, when silica glass is used as a glass starting material to obtain a high-purity oxynitride glass, it is necessary to carry out a nitriding treatment of the glass starting material at an extremely high temperature, which means that it is disadvantageous in terms of costs. Also, there is reported a method of producing oxynitride glass by subjecting Vycor glass or a dry gel obtained by a sol-gel method to an ammonia gas treatment. In this case, the resulting oxynitride glass suffers from the generation of pores.